The question was if any forum members had experienced a MSD (Manual Service Disconnect) service on their Bolt EV.

I recently brought my 2017 Bolt EV in for a routine tire-rotation and 'courtesy' check when the dealer notified me they would need to order a new MSD to prevent a loss of propulsion. The vehicle had 22,000 miles. Here are the details.

The dealer and the tech were very cooperative and walked me through the error codes as well as showing me the failed part (MSD, LEVER, P/N 24291219). This is a large 400A 500V fuse mounted in a lever-latched disconnect under the rear-seat cushions. It functions as a final 'fail-safe' for shorts or malfunctions. (Note: at the full rated 150kW/200HP output, the 375V nominal battery should supply 400A [150kW=375V x 400A]. The fuse would probably begin to blow at some multiple of the rating, so it appears to rated safely within the operating specification.)

Inspecting the part, I saw the plastic and connector blades in a new, unworn condition. However, the fuse itself gave off that wondrous odor of overheated electrical connections. The technician explained that when they performed a road test, the MIL (Malfunction Indicator Light) came on at set the following DTCs (these are my notes from the paperwork and our conversation)

The dealer tech did not share the TSB #18-NA-225 noted by wonderbolt. He did say that it was not related to the Bolt EV, but more for Chevrolet hybrid drive trains. Trying to solve the MIL light issue, the technician cross-referenced the DTCs and did some homework on his own to look at the Manual Service Disconnect. Good call!

According to the dealer service manager, GM had requested my old part be quarantined and returned for further investigation.

It appears there may be another potential loss-of-power scenario for the Bolt EV that has nothing to do with the battery pack, but rather the main service disconnect fuse.

If any members hear or experience this type of warning and repair, it would be good to share.

The question was if any forum members had experienced a MSD (Manual Service Disconnect) service on their Bolt EV.

I recently brought my 2017 Bolt EV in for a routine tire-rotation and 'courtesy' check when the dealer notified me they would need to order a new MSD to prevent a loss of propulsion. The vehicle had 22,000 miles. Here are the details.

The dealer and the tech were very cooperative and walked me through the error codes as well as showing me the failed part (MSD, LEVER, P/N 24291219). This is a large 400A 500V fuse mounted in a lever-latched disconnect under the rear-seat cushions. It functions as a final 'fail-safe' for shorts or malfunctions. (Note: at the full rated 150kW/200HP output, the 375V nominal battery should supply 400A [150kW=375V x 400A]. The fuse would probably begin to blow at some multiple of the rating, so it appears to rated safely within the operating specification.)

Inspecting the part, I saw the plastic and connector blades in a new, unworn condition. However, the fuse itself gave off that wondrous odor of overheated electrical connections. The technician explained that when they performed a road test, the MIL (Malfunction Indicator Light) came on at set the following DTCs (these are my notes from the paperwork and our conversation)

The dealer tech did not share the TSB #18-NA-225 noted by wonderbolt. He did say that it was not related to the Bolt EV, but more for Chevrolet hybrid drive trains. Trying to solve the MIL light issue, the technician cross-referenced the DTCs and did some homework on his own to look at the Manual Service Disconnect. Good call!

According to the dealer service manager, GM had requested my old part be quarantined and returned for further investigation.

It appears there may be another potential loss-of-power scenario for the Bolt EV that has nothing to do with the battery pack, but rather the main service disconnect fuse.

If any members hear or experience this type of warning and repair, it would be good to share.

Thanks for the indication on the "Service Plug", or MSD, or whatever the manufacturers call it.

On a broader search, the service plug appears to be a rare, but persistent cause of propulsion failure. As you noted, it is mentioned in both the Toyota and Tesla versions of the RAV4 EV. It also appears in GM for Chevrolet Hybrids and the Chevrolet Spark.

The 2001 RAV4 EV propulsion architecture helped me understand the issue. (Remarkable how close the 2001 RAV4 EV is in concept to both Tesla and the Bolt EV...Conditioned batteries, HV power bus for key components, etc...) (see schematic)

The service disconnect or MSD always splits the battery pack into two isolated sections so that no voltage appears at the battery terminals.

The MSD is therefore part of the battery circuit and indistinguishable to the control and sense electronics. (For costs, you are not going to monitor a connector or a fused connector. These are assumed to be reliable.)

Any degradation of the MSD would be interpreted by the battery sensors as a problem. The estimated internal cell resistance of a 288 cell pack is on the order of ~150 milliohm (60 Volt drop at full throttle of 400A and 375V nominal). A failing MSD that introduced an additional ~100 milliohms to the circuit would cause an additional 40 volt drop.

The battery sensors may interpret this additional voltage droop as a battery fault and start the entire alarm chain.

(Note: even a 100 milliohm additional resistance in the MSD at normal cruising energy draw of 30kW means an energy loss of about nearly a kilowatt in the MSD (30kW/375V nominal) = 80A; W=I2R=80^2A x 0.1ohm=640W)

You may not see the loss at low energy delivery, but the effects would be noted on acceleration or higher energy demands, like on a freeway or on an uphill. Just an ideal failure scenario!

640W into a 3-inch fuse will heat it up and make it smell bad, as mine was!

I wonder if this will appear more often as the Chevrolet Bolt EV fleet ages?

Registered

Thanks for the indication on the "Service Plug", or MSD, or whatever the manufacturers call it.

On a broader search, the service plug appears to be a rare, but persistent cause of propulsion failure. As you noted, it is mentioned in both the Toyota and Tesla versions of the RAV4 EV. It also appears in GM for Chevrolet Hybrids and the Chevrolet Spark.

The 2001 RAV4 EV propulsion architecture helped me understand the issue. (Remarkable how close the 2001 RAV4 EV is in concept to both Tesla and the Bolt EV...Conditioned batteries, HV power bus for key components, etc...) (see schematic)

The service disconnect or MSD always splits the battery pack into two isolated sections so that no voltage appears at the battery terminals.

The MSD is therefore part of the battery circuit and indistinguishable to the control and sense electronics. (For costs, you are not going to monitor a connector or a fused connector. These are assumed to be reliable.)

Any degradation of the MSD would be interpreted by the battery sensors as a problem. The estimated internal cell resistance of a 288 cell pack is on the order of ~150 milliohm (60 Volt drop at full throttle of 400A and 375V nominal). A failing MSD that introduced an additional ~100 milliohms to the circuit would cause an additional 40 volt drop.

The battery sensors may interpret this additional voltage droop as a battery fault and start the entire alarm chain.

(Note: even a 100 milliohm additional resistance in the MSD at normal cruising energy draw of 30kW means an energy loss of about nearly a kilowatt in the MSD (30kW/375V nominal) = 80A; W=I2R=80^2A x 0.1ohm=640W)

You may not see the loss at low energy delivery, but the effects would be noted on acceleration or higher energy demands, like on a freeway or on an uphill. Just an ideal failure scenario!

640W into a 3-inch fuse will heat it up and make it smell bad, as mine was!

I wonder if this will appear more often as the Chevrolet Bolt EV fleet ages?

Well... The TSB clearly states "applies to the 2017 Chevy Bolt" and in error code bingo, three of the codes match those in the title of the TSB "one or more of the following". I hope that @drdiesel1 or someone else with access can comment on the TSB content.

Registered

Very well written, @Pike Bishop. Thank you for sharing this breaking news about a potential new recall for our Bolts. Hope GM and the dealer gave you a nice Bolt or Volt as a loaner while you are out your Bolt.

Registered

Just registered so I could reply to this thread. I actually had the MSD fuse fail on my car while I was driving. Happened July 3rd on my way to work, in one of the worst places it could have happened... in the right turn lane that goes onto the freeway.

I was going about 35 mph and took my foot off the pedal to slow down (driving in L mode) for the lineup of cars waiting to get on the freeway. The cars in front of me stopped quicker than I expected so I used the brake pedal to slow down faster and just as I was slowing down with the brake, I felt the pedal sink down a bit as if the regen braking went away completely and then heard a *ding* from the car with a warning on the dash about "propulsion power is reduced". I came to a stop and the car said to put it in park, so I did. And then I tried to start again but it said something about "conditions not right for selected drive mode". I couldn't even shift it into neutral. Turning the car off and on again made no difference, but that brought up more warnings about servicing all sort of things on the car (cruise control, battery service, etc.). The range went from 244 miles down to 0, and then every once in a while would show 244 again, but eventually went to 0 for good.

Called the local police to get a car behind me with his lights on so I wouldn't get crashed into and so people would know to get over and go around me, and about 45 minutes later my tow truck finally came and towed me to the dealer. At this time, the backup that I had caused probably stretched for a mile... Sorry commuters... Anyway, the service department looked at it that day and told me the fuse in the Manual Service Disconnect failed, and that apparently there was a "bad batch" and they would be sending the old one to GM for analysis. Two days later (because of July 4th holiday) I got a new MSD and was back in business.

The scary thing was that when it failed, it lost all propulsion power. I could still steer and brake, but I was thinking that if I was on the freeway when it happened, I'd be in a very dangerous place that I wouldn't be able to get out of without a tow truck. So basically, if it happens while you're driving, get off the road as quickly and as safely as you can. Hopefully GM can determine what cars have the bad batches and issues a recall quickly.

Registered

I actually had the MSD fuse fail on my car while I was driving. Happened July 3rd on my way to work, in one of the worst places it could have happened...

... Anyway, the service department looked at it that day and told me the fuse in the Manual Service Disconnect failed, and that apparently there was a "bad batch" and they would be sending the old one to GM for analysis. Two days later (because of July 4th holiday) I got a new MSD and was back in business.

Registered

Called the local police to get a car behind me with his lights on so I wouldn't get crashed into and so people would know to get over and go around me, and about 45 minutes later my tow truck finally came and towed me to the dealer. At this time, the backup that I had caused probably stretched for a mile... Sorry commuters... Anyway, the service department looked at it that day and told me the fuse in the Manual Service Disconnect failed, and that apparently there was a "bad batch" and they would be sending the old one to GM for analysis. Two days later (because of July 4th holiday) I got a new MSD and was back in business.

The scary thing was that when it failed, it lost all propulsion power. I could still steer and brake, but I was thinking that if I was on the freeway when it happened, I'd be in a very dangerous place that I wouldn't be able to get out of without a tow truck. So basically, if it happens while you're driving, get off the road as quickly and as safely as you can. Hopefully GM can determine what cars have the bad batches and issues a recall quickly.

Good thinking there on calling the police to help you out. Thankfully nothing happened to you. You're the 3rd person on the forum thus far to experience the MSD issue. What's the build date on your Bolt? (going on the "bad batch" comment from your service department)

Registered

The question was if any forum members had experienced a MSD (Manual Service Disconnect) service on their Bolt EV.

I recently brought my 2017 Bolt EV in for a routine tire-rotation and 'courtesy' check when the dealer notified me they would need to order a new MSD to prevent a loss of propulsion. The vehicle had 22,000 miles. Here are the details.

Registered

I have a strong suspicion that it's not what you'd consider to be a "user-servicable part". Particularly since it appears that it's on a GM "restricted" list that requires the service tech to consult with head office before being allowed to order it.

The issue is likely that if a 400A fuse blows then you really, really want to make sure the problem is in the fuse itself and not downstream where that 400A is being transmogrified into work.

Registered

It's been a while for me since Driver's Ed, but I recall the first thing to do is NOT PANIC. The gist was with whatever forward momentum you still had try to merge to the shoulder. Hazards help but ultimately, if there's no hole in traffic and you've lost all momentum, just sit there in the lane with your hazards one. Some one will eventually complain about you or better yet, call the police yourself. Don't get out of your car on a busy freeway and keep that safety cage around you.

That's what I was taught way back when. Curious how others would handle such a situation.

Registered

It's been a while for me since Driver's Ed, but I recall the first thing to do is NOT PANIC. The gist was with whatever forward momentum you still had try to merge to the shoulder. Hazards help but ultimately, if there's no hole in traffic and you've lost all momentum, just sit there in the lane with your hazards one. Some one will eventually complain about you or better yet, call the police yourself. Don't get out of your car on a busy freeway and keep that safety cage around you.

That's what I was taught way back when. Curious how others would handle such a situation.

This. It's why I always try to be in the #1 (left) lane because on most freeways there is at least a partial emergency breakdown lane. You can also travel in the rightmost lane, but there's lots of entering and exiting vehicles, so I don't feel as safe there.

I once had a rear tire blowout on a motorcycle in the #1 lane without a breakdown lane and managed to make it to the right shoulder, but that was a while ago and traffic wasn't so solid as it is now. (SF Bay Area).

Registered

I have a strong suspicion that it's not what you'd consider to be a "user-servicable part". Particularly since it appears that it's on a GM "restricted" list that requires the service tech to consult with head office before being allowed to order it.

The issue is likely that if a 400A fuse blows then you really, really want to make sure the problem is in the fuse itself and not downstream where that 400A is being transmogrified into work.

Yeah. You'd need to disconnect the 12 volt battery, wear pressure tested rubber gloves, under leather gloves, and eye protection just to remove it. And as you said, you'd need to make dang sure that there was a faulty fuse BEFORE trying to put in a replacement. Or you could just put in a piece of copper bar stock, and watch for the smoke, to diagnose the source of the problem. :-(

Registered

I was recently contacted by the NHTSA for further information on the loss of power due to the MSD.

Loss of Motive Power / Propulsion / Stallingfor the Chevrolet Bolt EV is part of ODI (Office of Defects Investigation) case 2385A. ODI's questions asked if the vehicle had been repaired or if there were ongoing defects. It seems very routine.

[Since the MSD failure at 22,000 miles, the Bolt has not had any problems. Battery capacity looks great, and due to a work assignment, I am using the car for a bi-weekly 400 mile commute.]

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